Recycling used oil, often referred to as re-refining used lubricating oil is a little known process to the general public, re-refining is a proven industrial process for producing high quality lubricants and has been around for some time. Processing used oil, motor oil for example, into re-refined oil lubricants such as Group I, II, III base oil or vacuum gas oil (non-hydrotreated) generally involves collection, filtration, dehydration, distillation, hydrotreatment and fractionation (if necessary). Prior to used motor oil being re-refined into base oil and vacuum gas oil (VGO) a variety of processes are used to reduce the contaminant particles, organic metals, and chemical additives which include polymers that are present in the used motor oil.
A problem for re-refiners is the presence of chemical additive polymers in synthetic oil (Polyalpha-olefin), semi-synthetic oil, and blended base oil. For example, additives are introduced to base oils. These can include rust and corrosion inhibitors, detergents, dispersants, antifoaming agents, oxidation inhibitors, extreme pressure additives, and viscosity index improvers such as Olefin co-polymers (OCP) and Styrene/diene co-polymers. Expensive equipment that is used in the process of recycling used motor oil into base oil or vacuum gas oil become fouled by these additives. This causes failure of vacuum distillation and hydrotreating equipment. Because these polymers are not removed from the vacuum gas oil they adversely affect hydrotreating processes and oil blend performance, such as that of marine fuel.
One method of removing unwanted particles from used oils is with chemicals. Processors, particularly re-refiners, add chemicals during a pretreatment and post dehydration phase of oil processing to remove impurities from oil, such as vacuum gas oil. Chemical treating at this early stage of such processes removes metals but does not remove polymers (i.e. de-polymerize) from vacuum gas oil. Another method for removing impurities is by the use of clay and bauxite to filter the vacuum gas oil prior to hydrotreating. This process does not remove the polymers and generates waste solids causing a difficult and expensive disposal and environmental hazards. Another spent polymer removal method is by storing vacuum gas oil under a nitrogen blanket in an attempt to de-polymerize the vacuum gas oil. This only removes oxygen from the vacuum gas oil and does not remove polymers. Either of these processes would result in a product that remains polymer saturated and fouls up a hydrotreating process. This complex problem warrants further explanation.
Through a hydrotreating process, vacuum gas oil (“VGO”) is introduced to at least one catalyst reactor bed and subjected to hydrogen under high temperature and pressure to produce base oils. The base oils can then be hydrotreated, fractionated and blended with appropriate chemical additives specific to an end use, hydraulic or motor oil for instance, and then sold. The problem is that particles, polymers for example, found in the VGO prior to the hydrotreating process cause the catalyst reactor bed to foul prematurely.
Explaining an example of this problem further, in a typical hydrotreating process, ceramic support balls are loaded into the bottom of a vessel, referred to as a reactor, to provide support for a catalyst and to filter oil to be treated, VGO for instance. The vessel is then filled with a catalyst and then more support balls for filtering and distribution of an influent oil/hydrogen mix. This forms catalyst reactor beds designed to remove metals by bonding those metals to the catalysts. However, the catalyst is not used for removing polymers. The typical hydrotreating process will involve first reactors, or guard beds, with a less expensive catalyst used for reducing the metals and attempting to remove some polymers present in the vacuum gas oil, resulting in a partially treated VGO. Importantly, the partially treated VGO still contains polymers. The partially treated VGO carries these remaining polymers to expensive final stage reactors. Catalyst reactor beds in those final stage vessels clog with these remaining polymers and a pressure drop occurs. When these reactor beds experience this pressure drop, support balls and catalysts must be changed out resulting in product loss and high maintenance costs. In a typical used motor oil re-refining process, for instance, the hydrotreating reactor beds need to be changed out every one to six months. Notably, in a crude oil hydrotreating process, catalyst reactors operate for a few years without change because crude oil does not have fouling particles, such as manmade chemical additive polymers that are present in used motor oil.
Clearly, re-refiners using a hydrotreating process for VGO must regularly maintain the hydrotreating vessels, such as by changing out the catalyst reactor beds, because of polymer clogging, fouling. Changing out these catalyst beds is expensive and decreases revenue because the process must be halted.
Another problem in the oil re-refining and crude oil refining industry is the introduction of impurities into mixed oil end use products. For example, vacuum gas oil and crude vacuum gas oil is blended with fuels to make a marine oil, which is an oil blend. Marine oil is distributed for use in diesel marine combustion engines Crude vacuum gas oil and non-treated re-refined vacuum gas have some of the same characteristics except that no chemical additives are present in crude oil. However, troublesome impurities such as sludge and asphaltene-like compounds are found in both streams which may settle in ship bunkers and eventually clog filters and deposit on engine parts. In order to remove these impurities, centrifuges and clarifiers may have to be incorporated in the ship's hull prior to engine combustion. Another problem is the introduction of sulphur into the atmosphere from the use of fuel oils.
For the foregoing reasons, there is a need in the used oil re-refining industry for a process which will completely, efficiently, and cost effectively eliminate spent lubricant additives as part of the re-refining process. A process whereby saturated polymers in post-distillation vacuum gas oil are substantially removed. Additionally, the needed process should be such that organic impurities (e.g. asphaltenes, zinc, magnesium, phosphor and sulphur) are considerably reduced in the vacuum gas oil prior to distribution for marine fuel operations or hydrotreating. By such a needed process, hydrotreating and marine fuel operations should be greatly optimized by the use of the process' treated vacuum gas oil through lower operational costs, improved product quality and sales while at the same time emitting less sulfur to the atmosphere. Current re-refining operations should be retrofittable with the needed process incurring minimal equipment costs resulting in substantial operational cost savings rapidly off-setting the retrofit costs. There is also a need in the industry for a VGO with superior non-obstructing qualities useful in fuel oil blends and for reducing pollution.